1. Technical Field
The present disclosure is directed to electrosurgical apparatus, methods and systems, and, in particular, to an electrosurgical return pad that provides even heat and current distribution and cooling.
2. Background of Related Art
During monopolar electrosurgery, a source or active electrode delivers energy, such as radio frequency energy, from an electrosurgical generator to the patient and a return pad carries the current back to the electrosurgical generator. The source electrode is typically placed at the surgical site and high density current flows from the source electrode to create the desired surgical effect of cutting and/or coagulating tissue. In tissue ablation, another form of electrosurgery, the source electrode or electrodes are typically placed in or adjacent the target tissue and high density current flows through the target tissue thereby destroying the target tissue. The patient return pad is placed at a distance from the source electrode and may be in the form of a pad adhesively adhered to the patient.
The return pad typically has a large patient contact surface area to minimize heating at that return pad site. The larger the contact area between the return pad and patient skin, the lower the current density and the lower the intensity of the heat. The size of return pads is based on assumptions of the maximum current seen in surgery and the duty cycle (e.g., the percentage of time the generator is on) during the procedure. The first types of return pads were in the form of large metal plates covered with conductive jelly. Later, adhesive electrodes were developed with a single metal foil covered with contact layer formed of conductive jelly, conductive adhesive or conductive hydrogel.
One issue with these adhesive electrodes was that current flow from the active electrode concentrates at the leading edge, the edge of the return pad closest to the active electrode, causing a heating imbalance across the return pad. This phenomenon, known as “Leading Edge Effect” can cause tissue change or injury if the skin under the leading edge portion of the return pad is heated beyond the point where circulation of blood can cool the skin.